The invention relates to a new covering agent for sealing microscopy specimens.
Covering agents for sealing microscopy specimens are known and are in use in histology and cytology. Cytochemical and immuno-histochemical preparations are usually first mounted on a microscope slide, fixed if required and/or stained by special methods for the better differentiation of intracellular constituents. They are then sealed with a covering agent. Alternatively, it is possible to carry out staining and sealing at the same time (German Auslegeschriften 2,635,438 and 2,635,449 and German Offenlegungsschrift 2,737,845).
Covering histochemical and cytochemical specimens requires the use of aqueous covering agents, since certain color-bearing substances are dissolved when organic solvents are used, whereby the staining of the specimens is destroyed.
Aqueous covering agents are known. They are based on water-soluble organic polymers, such as gelatin, polyvinylpyrrolidone or polyvinyl alcohol. The covering agents used hitherto are not satisfactory for various reasons. Covering agents containing gelatin must, for example, be liquefied by warming before being used.
If synthetic polymers are used as the base polymer, a customary acid or base is added to the aqueous polymer solution for the neutralization which is required. An example of a customary base is sodium hydroxide solution or aqueous ammonia solution.
Although covering agents of this type retain in part the specific staining of the cytochemical process, the counter-staining of the cell nucleus obtained with hemalum fades very rapidly.
If, for example, in order to detect the peroxidase reaction in leucocytes, the fixed and stained smears of blood or bone marrow are covered with glycerol gelatin or with a covering agent based on polyvinyl alcohol, after 3 weeks the nuclear staining has faded and the peroxidase staining has disappeared. Without a covering agent the black-brown granules in peroxidase-positive cells are stable for approximately 3 days, and, when covered with immersion oil, are stable even for only a few hours.
If a fixed and stained smear of blood or bone marrow intended to detect the 1-naphthyl-acetate esterase reaction in leucocytes is covered with glycerol gelatin, after 3 weeks the nuclear staining has faded. Without covering, the red-brown granules in esterase-positive cells are stable for approximately 5 days, or for only a few hours when directly covered with immersion oil.
Problems also arise in covering immuno-histochemically stained specimens with respect to retention of color. A process used for the detection of immunoglobulin G in a tonsil section is, for example, rendering peroxidase visible by incubation with 3-amino-9-ethylcarbazole. Here, too, the nuclear staining fades in the course of a few weeks after being covered with glycerol gelatin. In addition, a considerable formation of bubbles is observed in the specimen.
It is as yet not known to obtain an aqueous covering agent for microscopy specimens which is capable of indicating colorations in intracellular constituents for a substantially longer time than in the above examples.